EWD devices adjust the amount of light to be transmitted by means of electrocapillarity (electro-wetting). EWD devices display images with excellent brightness and contrast, and relatively low power consumption compared to many other display devices.
Referring to FIG. 6, this is a cross section view of part of a conventional EWD device before a voltage is applied thereto. The EWD device 10 includes a first substrate 11, a second substrate 18 facing towards the first substrate 11, an first fluid 15, a second fluid 16, a plurality of partition walls 14 and two support plates (not shown). The two support plates are provided between the two substrates 11, 18 for supporting the transparent substrate 11. Thereby, the two substrates 11, 18 and the two support plates define a sealed container (not labeled) to be filed with the first fluid 15 and the second fluid 16. A hydrophobic insulator 13, a driving circuit layer 12 and the second substrate 18 are stacked one on the other in that order from the top to the bottom. The partition walls 14 are arranged in a lattice on an inner surface of the hydrophobic insulator 13 thereby defining a plurality of pixel regions R. The first fluid 15 sealed within the sealed container corresponding to the pixel regions R is an opaque fluid. The second fluid 16 immiscible with the first fluid 15 is contacted to the first fluid 15 and filled in the sealed container.
Referring to FIG. 7, the driving circuit layer 12 includes an active driving circuit (not labeled) and a passivation layer (not shown) covering the active driving circuit. The active driving circuit includes a plurality of first driving lines 121 that are parallel to each other and that each extends along a first direction, a plurality of second driving lines 122 that are parallel to each other and that each extends along a second direction orthogonal to the first direction, a plurality of thin film transistors (TFTs) 124 that function as switching elements, and a plurality of pixel electrodes 125. The first driving lines 121 and the second driving lines 122 cross each other and correspond to the partition walls 14, thereby defining a plurality of rectangular areas (not labeled) corresponding to the pixel regions R. Each of the TFTs 124 is provided in the vicinity of a respective point of intersection of the first driving line 121 and the second driving line 122, and includes a gate electrode 126, a source electrode 127 and a drain electrode 128. The gate electrode 126, the source electrode 127 and the drain electrode 128 are connected to a corresponding first driving line 121, a corresponding second driving line 122, and a corresponding pixel electrode 125 respectively. Each pixel electrode 125 is continuously located on a remaining region of a corresponding rectangular region where no TFT 124 is present.
When no voltage is applied, the first fluid 15 extends over an entire area in a direction that is orthogonal to the direction in which light is transmitted. Therefore, the light is shielded by the first fluid 15 and the EWD device 10 displays a black image.
When a signal voltage is applied to one of the pixel electrodes 124 by the corresponding TFT 125 and a common voltage is applied to the second fluid 16, an electric field is generated between the second fluid 16 and the pixel electrode 125. On the other hand, a lower left hand corner of the rectangular region where the TFT 124 is present is a non electric field area, and thus the hydrophobic insulator 13 corresponding to the TFT 124 remains less wettable. As a result, an interface between the first fluid 15 and the second fluid 16 changes due to electrocapillarity, so that the first fluid 15 moves towards the lower left hand corner and the second fluid 16 contacts the hydrophobic insulator 13. Light emitted from the first substrate 18 passes through the second fluid 16, and the EWD device 10 displays a white image.
However, sometimes the EWD device 10 is not quick enough to shift from an off state to an on state, when the first fluid 15 moves towards the lower left hand corner.
What is needed, therefore, is an EWD device that can overcome the above-described deficiencies.